Friendly fungus helps keep aflatoxin out of cotton

In a brutal battle for food and space, two fungal cousins are currently duking it out across the nation's cotton fields. Thanks to biological control strategies developed by the Agricultural Research Service, the better of these two microscopic relatives is winning.

Plant pathologist Peter Cotty, who is part of the ARS Food and Feed Safety Research Unit at New Orleans, La., but is located at the University of Arizona-Tucson, instigated this competition. By pitting a benign strain of Aspergillus against its noxious kin, he's helping rid U.S. cotton of a harmful and costly toxin.

While invisible and odorless, the Aspergillus fungi that Cotty is focused on can churn out potent poisons called alfatoxins. These carcinogenic compounds — linked to impaired growth, cancer and death — would threaten human health if stringent food safety standards, set by the U.S. Food and Drug Administration, weren't in place to screen out contaminated products.

When cottonseed becomes infested with toxin-making fungi, it must be discarded or severely downgraded. That's because the seed is a major feed of dairy cows, and any toxins that might be present could transfer to the animals' milk. Every year, aflatoxin is responsible for ruining $3 million to $8 million worth of cottonseed in the American Southwest.

Knowing that few control options exist for farmers, Cotty set out two decades ago to find an environmentally sound and effective solution. Eventually, he discovered one, in the form of a benign strain of Aspergillus flavus that, when applied correctly to cotton fields, can outgrow and outlive its more menacing cousins.

After years of rigorous studies with the strain, which is dubbed AF36, ARS obtained approval from the U.S. Environmental Protection Agency in 1996 to test the new biocontrol in Arizona cotton fields.

At that time, only 120 acres of commercial cotton were treated with AF36. Now, more than 100,000 acres of U.S. cotton have been treated, greatly reducing levels of harmful aflatoxins.